1. Field of the Invention
Aspects of the present invention relate to an electrode for a fuel cell, a membrane-electrode assembly for a fuel cell, and a fuel cell system including the same. More particularly, aspects of the present invention relate to an electrode for a fuel cell that will produce a fuel cell with high efficiency and high power because of high catalyst efficiency, as well as a membrane-electrode assembly for a fuel cell, and a fuel cell system including the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and hydrogen in a hydrocarbon-based material such as natural gas or an alcohol such as methanol, ethanol, propanol or butanol.
Such a fuel cell is a clean energy source that may replace fossil fuels. It includes a stack composed of unit cells and produces various ranges of power output. Since it has a four to ten times higher energy density than a small lithium battery, it has been promoted as a small portable power source.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell, which uses methanol as a fuel.
The polymer electrolyte fuel cell has the advantage of a high energy density, but it also has problems in the need to carefully handle hydrogen gas and the requirement of accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as the fuel gas.
Conversely, a direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte fuel cell, but it has the advantages of easy handling of the fuel, being capable of operating at room temperature because of its low operating temperature, and no need for additional fuel reforming processors.
In the above polymer electrolyte fuel cell, the stack that generates electricity generally includes several to scores of unit cells stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) attached to each other with an electrolyte membrane between them.
The fuel is supplied to the anode and absorbed in the anode catalyst, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into the cathode via an external circuit, and the protons are transferred into the cathode through a polymer electrolyte membrane. An oxidant is supplied to the cathode, and the oxidant, protons, and electrons are reacted on a catalyst at the cathode to produce electricity along with water.